1. Field of the Invention
This invention relates to a fluid pump system for ink jet printer apparatus.
2. History of the Prior Art
The use of nonimpact endorsers requires a supply of printing fluid to an ink jet printer apparatus. The prior art has generally utilized a piston driven positive displacement fluid pump to circulate printing fluid through an ink jet printer system. These positive displacement fluid pumps suck fluid from a reservoir during piston travel in one direction and expel the fluid into the ink jet printer system during piston travel in the opposite direction. However, this alternating pumping action creates fluid pressure pulses which must be dampened to provide the required steady fluid flow to the ink jet printer apparatus. The effect of the fluid pressure pulses is often minimized by adding fluid accumulators to an ink jet printer system. These components absorb a pulse of fluid upstream from the ink jet printer apparatus so that a steady flow of pressurized fluid is available for accurate printing at the ink jets. Nevertheless, obvious drawbacks to such a system are the cost and space requirements of the components.
Quality nonimpact endorsement systems depend upon a continuous source of contaminant and air-free fluid since characters are printed with individual drops of fluid. The introduction of air into the fluid supply can result in a droplet stream gap with air replacing a fluid drop. Aerated fluid may also cause sporadic losses of fluid pressure due to the increased compressibility of an air-fluid mixture relative to a pure fluid. The pressure loss may then be manifested by slower fluid drops from the ink jet printer apparatus which consequently form improperly shaped characters on a printing surface.
Some systems separate the air from the printing fluid with air traps, air purge valves, vacuum pumps, filters, and fluid preheaters. Printing fluid is heated to cause the air in the fluid to precipitate out of solution as small air bubbles. These collect into larger bubbles which are less dense than their surrounding fluid. The natural buoyancy forces cause the larger air bubbles to rise to the surface of the printing fluid where suction from a vacuum pump removes the air from the system upon the actuation of an air purge valve. An alternative to heating the fluid is to force the liquid through a fine filter. Tiny air bubbles are squeezed out of the fluid passing between the particles comprising the filter. The tiny, close air bubbles then draw together by Van Der Waals' intermolecular forces to form larger air bubbles and float to the fluid surface where they are vented from the system when an air purge valve is opened. As with the positive displacement fluid pump, accumulators and shock dampening components are needed to stabilize the fluid pressure during the periodic venting of accumulated air upon the opening of an air purge valve.
The disclosed invention supplies a necessary flow of pressurized, contaminant and air-free fluid to an ink jet printer apparatus with a system costing less in money, maintenance, and space. In addition, the design of the invention eliminates pressure shocks from fluid pumping and deaeration in a nonimpact endorser system to permit controlled printing of quality characters.